Various devices for protecting plants against frost damage are known in the art. They include devices that cover plants to retain solar-thermal or geo-thermal energy and devices that generate heat, such as gas-fired heaters used in the citrus and other industries. Devices that collect or retain solar-thermal or geo-thermal energy include greenhouses, various framed structures with translucent covering, and smaller, portable translucent devices. The present invention relates primarily to the latter.
The prior art includes at least two portable plant protecting devices that are configured to provide frost protection, yet support ventilation as temperatures rise. One is U.S. Pat. No. 3,946,521, issued to Ours for a Ventilated Plant Protector. The other is U.S. Pat. No. 5,669,177 issued to Frounfelker (the inventor herein) for a Thermal Controlled Plant Protector. The '177 patent improved over the '521 patent, and the present invention improves over the '177 patent.
One disadvantageous aspect of the device of the '177 patent is that it may experience mechanical failure. The member that covers the ventilation openings is provided on the exterior of the housing. When handled roughly, this cover is readily dislodged or jammed or develops increased friction and no longer moves as desired. The exposed cover is also susceptible to fouling from environmental debris or other objects: leaves, twigs, dirt, insects, etc., that fall onto or otherwise become coupled to the cover. Furthermore, when stored in any position other than upright, the exposed cover may become dislodged or bent or otherwise impacted such that it fails to operate properly. The device of the '521 patent also has an exposed cover and suffers from the same or similar problems.
The device of the '177 patent (and that of the '521 patent) is also disadvantageous in that it is relatively difficult and expensive to manufacture. This is due primarily to the deep cavity design and the difficulty of forming such designs via injection molding techniques. In addition, the device of the '177 patent is disadvantageous in that the design may include stress points that are undesirably prone to failure, due either to insufficiently supported structures or angles or other structurally fragile aspects.
The device of the '177 patent (and that of the '521 patent) is further disadvantageous in that due to the externally disposed configuration of the airflow control shield there is a higher likelihood of damage and failure during stacking and storage.
A need exists for a thermal controlled plant protector that significantly reduces the incidence of mechanical failure, is durable when handled roughly, is resistant to failure from environmental debris/conditions and is readily stackable, at various angles, and with a high probability of functioning correctly after removal from the storage stack.